System, apparatus and method for dispensing chemical vapor

ABSTRACT

This invention relates to a system for testing the operation of a detection instrument, which comprises a first enclosure having at least two ports and containing a fluid comprising a substance detectable in gas form by the instrument, said fluid being present in part as a vapor phase and in part as a liquid phase in equilibrium with one another, said first enclosure being interconnected with the instrument such that the fluid contained in the first enclosure can be dispensed to the instrument via at least one port of said first enclosure; a second enclosure having at least one port and containing either the same or a different fluid in gas form as compared with the first enclosure, said second enclosure being adapted for selective dispensing of a known or ascertainable mass of the fluid contained therein via at least one port thereof, and being interconnected with the first enclosure such that said mass can be introduced into the volume within said first enclosure through at least one port thereof, thereby to displace a correlative mass of the vapor phase fluid contained in the first enclosure causing said correlative mass to be dispensed to said instrument; and a valve in communicating relationship with said first enclosure and positioned such that, when the first enclosure is interconnected with said instrument, the valve is interposed between the interconnected first enclosure and instrument, which valve is capable of selectively permitting flow to said instrument of said vapor phase fluid dispensed from the first enclosure upon being displaced by said introduction of fluid from the second enclosure; the invention also relates to apparatus for implementing and a method involving same.

FIELD OF THE INVENTION

The invention relates to technology for verifying the proper operationof a detection instrument, through release of a known or ascertainablevolume of a vapor.

BACKGROUND OF THE INVENTION

Instruments for the detection (including quantitative detection ormonitoring) of gaseous chemical species require periodic checking withknown reference gas samples to verify their correct operation. Variousways of providing a suitable reference gas sample for calibrationpurposes are known. These methods include the use of pre-mixedcompressed gas standards, calibrated permeation tubes, diffusion tubes,and diluted vapor bubblers.

While some of these alternatives are capable of very high precision andaccuracy, known calibration technology tends to be costly, entailsinconvenient operations, or requires cumbersome supporting hardware (forexample, ovens, pumps, and flowmeters), and is thus impractical for ahandheld, low maintenance, or low cost instrument.

A vapor is the volatile, gaseous fraction of a chemical species thatexists as a liquid at room temperature and ambient pressure. A verysimple and attractive way to generate a vapor is to put the liquidchemical into a partially filled, closed container and allow itsheadspace to reach equilibrium. At equilibrium, the concentration of theheadspace vapor will be dependent on the temperature and pressure of thecontainer and the composition of its contents. The vapor activity of achemical is defined as the ratio of the partial pressure of the vapordivided by the saturated pressure of the chemical at a giventemperature. Therefore, the activity of the vapor at equilibrium withits liquid state in a closed container will have a numerical value equalto one at any given temperature. This means the saturated headspacevapor concentration is a quantitatively reproducible value at a knowntemperature and pressure.

A difficulty associated with using saturated headspace vapor for thetesting and calibration of most chemical detection instruments is thatthe headspace vapor is usually much too concentrated. In addition, theremoval of a large vapor sample from a closed container will result in asevere departures from equilibrium conditions unless the ratio of thevolume of the container to the volume of headspace vapor removed isrelatively large. Consequently, most instruments require a vaporreservoir of substantial volume to provide a reproducible vapor samplesuitable for analysis.

If one could remove a reproducible, small volume from the saturatedvapor headspace, then near-equilibrium conditions could be maintained,and a small mass of vapor, appropriate for the sensitivity of theinstrument to be calibrated, could be delivered. The problem is todevise a method whereby a small, reproducible volume of vapor can bedispensed from the reservoir containing the saturated headspace vapor.

The most common method involves the use of a microliter syringe. In thismanual method, the user inserts a small needle through a rubber septumseal to the vapor container and removes a small aliquot of the headspacevapor. While effective, this method is not well suited for automatedoperation unless very large and expensive auto-injector robotic systemsare employed. See U.S. Pat. No. 5,792,423 (Markelov).

Other methods rely upon the use of stripper gas (also referred to as a“purge” or “carrier” gas), such as nitrogen, to “sweep” a sample of theheadspace vapor to a dispersal site, usually a measurement instrument.For instance, see U.S. Pat. No. 5,363,707 (Augenblick et al.), U.S. Pat.No. 6,365,107 (Markelov et al.), U.S. Pat. No. 6,395,560 (Markelov), orU.S. Application Publication No. US 2004/0040841 (Gonzalez-Martin etal.). Another method involves allowing a heated liquid to enter thesample vessel and displace the headspace vapor. See U.S. Pat. No.6,286,375 (Ward).

Because of the drawbacks attendant upon the above-mentioned approaches,provision of a technology which permits effective testing of a detectioninstrument while ameliorating such drawbacks would be a significantadvance.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a system, apparatus andmethod for generating small amounts of vapor from chemical species thatare liquids or low volatility solids at normal operating conditions.

It is another object of the invention to provide a system, apparatus andmethod for generating small amounts of vapor suitable for thecalibration of high sensitivity detection instruments.

It is yet another object of the invention to provide a system forgenerating small amount of vapors that is compact and suitable forincorporation into a detection instrument, as well as apparatus forimplementing and a method involving same.

It is a further object of the invention to provide a system forgenerating small amounts of vapor that has an extended operating lifeand requires minimal maintenance, as well as apparatus for implementingand a method involving same.

SUMMARY OF THE INVENTION

In one aspect, the invention is a system for testing the operation of adetection instrument, which comprises a first enclosure having at leasttwo ports and containing a fluid comprising a substance detectable ingas form by the instrument, said fluid being present in part as a vaporphase and in part as a liquid phase in equilibrium with one another,said first enclosure being interconnected with the instrument such thatthe fluid contained in the first enclosure can be dispensed to theinstrument via at least one port of said first enclosure; a secondenclosure having at least one port and containing either the same or adifferent fluid in gas form as compared with the first enclosure, saidsecond enclosure being adapted for selective dispensing of a known orascertainable mass of the fluid contained therein via at least one portthereof, and being interconnected with the first enclosure such thatsaid mass can be introduced into the volume within said first enclosurethrough at least one port thereof, thereby to displace a correlativemass of the vapor phase fluid contained in the first enclosure causingsaid correlative mass to be dispensed to said instrument; and a valve incommunicating relationship with said first enclosure and positioned suchthat, when the first enclosure is interconnected with said instrument,the valve is interposed between the interconnected first enclosure andinstrument, which valve is capable of selectively permitting flow tosaid instrument of said vapor phase fluid dispensed from the firstenclosure upon being displaced by said introduction of fluid from thesecond enclosure.

In another aspect, the invention is an apparatus for dispensing a knownor ascertainable mass of a fluid in gas form to a detection instrument,comprising: a first enclosure adapted for interconnection with theinstrument and capable of containing said fluid when present in part asa vapor phase and in part as a liquid phase in equilibrium with oneanother; interconnected with the first enclosure, a second enclosurecapable of containing either the same or a different fluid in gas formas compared with the first enclosure, said second enclosure beingadapted for selective dispensing of a known or ascertainable mass offluid it is capable of containing for introduction into the volumewithin said first enclosure thereby to displace a correlative mass ofthe vapor phase fluid the first enclosure is capable of containing,causing said correlative mass to be dispensed to said instrument; and avalve in communicating relationship with said first enclosure andpositioned such that, when the first enclosure is interconnected withsaid instrument, the valve is interposed between the interconnectedfirst enclosure and instrument, which valve is capable of selectivelypermitting flow to said instrument of said vapor phase fluid dispensedfrom the first enclosure upon being displaced by said introduction offluid from the second enclosure.

In still another aspect, the invention is a method of dispensing to adetection instrument a known or ascertainable mass of a fluid in gasform comprising: in a first enclosure interconnected with saidinstrument and containing said fluid, maintaining conditions such thatthe fluid is present in part as a vapor phase and in part as a liquidphase in equilibrium with one another; in a second enclosureinterconnected with said first enclosure and containing either the sameor a different fluid in gas form as compared with the first enclosure,subjecting the fluid in the second enclosure to conditions sufficient toeffect an expansion of the fluid in gas form, such that a known orascertainable mass of said fluid in gas form is dispensed from thesecond enclosure and introduced into said first enclosure, thereby todisplace a correlative mass of the vapor phase fluid in the firstenclosure, causing said correlative mass to be dispensed to theinstrument; and selectively permitting said correlative mass to flowthrough to the instrument.

Practice of the invention results in substantial advantages. Theinvention is useful for generating small quantifiable aliquots of abroad spectrum of vapors. This includes, without limitation, anymaterial that is a liquid at the operating temperature of the apparatus.In addition, the invention can be used to generate vapors from variousmaterials that are low volatility solids. Practice of the invention isfurthermore very economical in terms of space requirements (for example,the apparatus of the invention is very compact, making it suitable forincorporation in the chemical instrumentation for which calibration issought). Moreover, the invention allows the simple generation of smallvolumes of vapor suitable for use with high sensitivity instruments (forinstance, microliter volumes). By dispensing small amounts of vapor, thelifetime of the reservoir from which the vapor comes is extended,thereby minimizing maintenance. Further, the volume of vapor dispensedis more easily controlled, such as by selecting the temperature ofequipment (for example, a pump system or other suitable component)inducing flow of the vapor amount. Thus, with the invention, one candeliver a precise vapor amount in a short period of time, on the orderof seconds.

These and other benefits conferred by the invention are described aswell in the following discussion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an embodiment suitable forchemical vapor dispensing according to the present invention.

FIG. 2 is a schematic diagram showing another embodiment suitable forchemical vapor dispensing according to the present invention.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

As indicated above, a central feature of the invention is provision of aknown or ascertainable vapor mass suitable for use in verifying theproper operation of a chemical detection instrument. This isadvantageously accomplished simply and repeatedly in accordance with theinvention, by displacing a desired mass of fluid from a pump module (asdiscussed in more detail hereinafter), which mass of fluid has aproportionally related volume, such that said volume flows to aninterconnected fluid reservoir where it displaces a like volume of fluidfrom said reservoir, said like volume of fluid in turn having aproportionally related mass that is known or ascertainable; the lattermass can then, for instance, be introduced into a detection instrument.It will be appreciated that, since such latter mass is related to thevolume displaced from the reservoir and therefore the volume—and themass—of the fluid displaced from the pump module, the mass of the fluiddisplaced from the reservoir is correlative with the mass displaced fromthe pump module. As used herein, the terms “correlative,”“correlatively,” etc., shall refer to the proportional (and calculable)relationship between the mass of fluid displaced from the reservoir andthe mass of the fluid displaced from the pump module. Practice of theinvention affords its practitioner a reliability of result, as well as areadiness and versatility of application, representing a significantadvance in the art.

Chemical vapor detection instruments which can be calibrated or the likein accordance with the invention are used in a wide variety ofapplications and industries, including the chemical, government,medical, food and beverage, semiconductor, automotive, pharmaceuticaland petroleum markets. More specifically, any of a wide variety of theseinstruments is suitable for practice of the invention; such instrumentstypically consist of a handheld or mountable apparatus capable ofdetecting the presence and/or concentration of a selected chemical vaporin an environment of interest. Some examples include surface acousticwave, gas chromatograph, and electrochemical cell array detectioninstruments and technologies. This reflects the invention's versatility.

That versatility is also reflected by the variations indetectioninstrument design which the invention accommodates. For instance, manychemical vapor detection instruments have a pump to pull at least asubstantial portion of a sample into the instrument for analysis. Whenthe detection instrument responds very quickly, then the inventionpermits one to establish, at least semi-quantitatively, whether or notthe instrument is responding properly to the vapor. Other detectioninstruments collect the entirety of a vapor sample and thus performdiscrete measurements on the whole sample, such that a quantitativecalibration of the instrument is feasible.

In accordance with FIG. 1, a preferred embodiment of the inventioncomprises a small first enclosure 20 containing a reservoir of thedesired vapor to be dispensed, an outlet conduit 10 from the enclosure,and a pump module 5. Such pump module is a highly advantageous featureof preferred embodiments of the invention, and is formed by acombination of components that operate to achieve the result sought.Thus, in FIG. 1, the pump module 5 comprises (inter alia) a secondenclosure 30 containing an air reservoir (connected to the firstenclosure 20 and the vapor reservoir contained therein), a heatingelement 40 in thermal contact with the second enclosure, and a sensor 53for ascertaining the amount of heat delivered to the air reservoir inthe second enclosure. Prior to operation, the vapor reservoir is allowedto remain in a quiescent state long enough to allow the headspacematerial in the second enclosure to reach saturated equilibrium with theliquid in that enclosure. Generally, the time required to reestablishvapor reservoir equilibrium after a heating cycle is brief (e.g.,several minutes), especially when small amounts of the reservoir (e.g.,less than 1%) are dispensed.

More specifically, in the embodiment depicted in FIG. 1, there is asmall pump module 5 to displace a precise mass of saturated vapor andcause it to be delivered to the instrument to be calibrated. The pumpincludes an air reservoir in enclosure 30 maintained at ambientpressure. The air reservoir in enclosure 30, via port 31, is incommunication with conduit 35, which is also in communication withenclosure 20 and the reservoir of saturated vapor contained therein, viaport 22. Enclosure 20 contains vapor and liquid in equilibrium, with thevapor occupying the headspace 24 within the enclosure. Ideally, thediameter and length of the conduit 35 will be chosen to minimize “dead”volume and to minimize diffusion when the pump module is off. Enclosure20 and the vapor reservoir contained therein are similarly incommunication with vapor outlet 10 via port 21 in enclosure 20. Vaporoutlet 10 is in communication with detection instrument 70.

Heating element 40 is located abutting, and in thermal contact with,enclosure 30. When the user desires that a vapor sample be sent to vaporoutlet 10, heating element 40 is energized to produce a predeterminedtemperature increase in the air reservoir in enclosure 30 that resultsin a predetermined amount of expansion of the air. A correspondingdesired mass of air with a proportionally related volume overflowsenclosure 30 into conduit 35, and travels into enclosure 20 and thevapor reservoir contained therein, thus displacing a like volume ofvapor (having a correlative and thus known or ascertainable mass) fromheadspace 24 into the vapor outlet 10.

Vapor reservoir enclosure 20 and air reservoir enclosure 30 beginoperation at the same temperature and pressure. When vapor is to bedispensed, heating element 40 is energized. The amount of heat providedby the heating element is regulated by temperature controller 50 (aprocessor) which sends signals to heating element 40 activating anddeactivating such element through heater control signal line 52 andreceives feedback from sensor 53 concerning the temperature of thecontents of air reservoir enclosure 30 via temperature signal line 51.

As the air in the fixed volume of the air reservoir is warmed, thepressure inside the air reservoir enclosure increases, causing theenclosed air to expand and a desired mass/volume thereof to betransferred through conduit 35 and into vapor reservoir 20, therebydisplacing a like volume of saturated headspace vapor into vapor outletconduit 10 and on to detection instrument 70. Conduit 35, which runsbetween air reservoir enclosure 30 and vapor reservoir enclosure 20,also serves to cool the displaced air from the air reservoir conduit 30so that it does not significantly disrupt the vapor equilibrium inheadspace 24 through an infusion of a substantial amount of heat.

The desired amount of air is induced to exit air reservoir enclosure 30,into conduit 35 and via same into vapor reservoir enclosure 20, bycausing the air of the reservoir to expand in corresponding amount viaintroduction of a predetermined amount of heat energy to the airreservoir. Heating element 40 is activated by temperature controller 50,and emits heat energy for an amount of time, such that the amount ofheat energy necessary to effect the desired amount of expansion istransferred to the contents of air reservoir enclosure 30, and then theheating element is deactivated. The amount of heat introduced can bemanaged by setting the duration of the heating period, or by keying suchduration to feedback from temperature signal line 51 concerning thetemperature of the air in the air reservoir. At the point the heatingcycle is concluded, expansion of the air in the air reservoir isarrested, the temperature of the air in the air reservoir decreases, andthe internal pressure in air reservoir enclosure 30 drops, and in turnthe pressure in vapor reservoir enclosure 20 also drops, causing ambientair to be drawn back into vapor output conduit 10. Thus, the systemeffectively “breathes out” when heat is applied and “breathes in” whenthe heat is removed.

In another preferred embodiment, shown in FIG. 2, air reservoir conduit130, heater 140, temperature controller 150, temperature signal line151, heater control signal line 152, and sensor 153 cooperate toprovide, in effect, pump module 105 which delivers a desired amount ofair to a vapor reservoir for the purpose of causing same to furnish aknown or ascertainable amount of vapor to an instrument of interest.Thus, there is an air reservoir enclosure 130, interconnected with avapor reservoir enclosure 120, by conduit 135 running between them; airflows from the air reservoir to the vapor reservoir within enclosure120. Vapor reservoir enclosure 120 is in turn interconnected via conduit125 to port 165 of three-way valve 160, which, in turn, isinterconnected with a vent 115 via conduit 161 and a vapor outletconduit 110 (which outlet is in communication with the instrument to becalibrated). In the normal position of three-way valve 160, theconnection through port 164 to vapor outlet conduit 110 is closed, andthe vapor reservoir will be cut off from the outlet to the instrument.In this regard, valve 160 ensures that small ambient temperaturevariations in the apparatus will not result in vapor reservoir's“breathing-out” vapor through vapor outlet conduit 110 to detectioninstrument 170.

Furthermore, in its normal position, three-way valve 160 provides anunobstructed path from the vapor reservoir through port 163 in valve 160to conduit 161, which leads to vent 115. Access to the ambientatmosphere results in pressure equalization between the vapor reservoirand the air reservoir, so that when the pump module 105 is activated,the volume produced by the air reservoir will be equal to the volumedisplaced from vapor reservoir. Additionally, since in its normalposition three-way valve 160 closes off communication with vapor outletconduit 110, the “breathe in” cycle of the pump bypasses conduit 110,thereby leaving the vapor occupying such path undisturbed and assuringhigher precision of the vapor volume delivered in the subsequent cycle.

The preferred embodiment uses an electrically activated heater and anelectrically controlled valve. Temperature control element 150 is aprocessor that governs the amount of heat delivered by activating andthereafter deactivating heating element 140 such that it either operatesfor a desired period of time or operates until the contents of airreservoir enclosure 130 reach the desired temperature as indicated tothe control element by feedback from sensor 153 received via temperaturesignal line 151 and then shuts off when the desired end temperature hasbeen reached. (Sensor 153 is preferably an electrical temperaturesensing device, for example, a thermocouple or thermistor; however, thesensor can consist of any device capable of delivering a temperaturefeedback signal to the temperature control element 150.) Likewise, theaction of valve 160 is controlled by a processor, which sends signals tothe valve causing it to move between the positions discussed in thepreceding paragraph. In the preferred embodiment, the temperaturecontrol element 150 electrically controls the operation of valve 160 bysending signals to the valve over valve control signal line 154.Effective results can be obtained if the operation of valve 160 iscorrelated with the application of heat to air reservoir enclosure 130.

In an advantageous variation, a wick is provided inside vapor reservoirenclosure 120 to store the liquid contents of the vapor reservoirenclosure. This eliminates the presence of neat liquid in the reservoirand the attendant problem that, when neat liquid is present, the properorientation of the reservoir must be carefully maintained at all timesor liquid might be allowed to flow into the outlet conduit withundesirable consequences. In contrast, the use of a wicking elementeliminates the need to maintain a particular gravitational orientationof the device. Of course, even when the liquid phase is “held” by thewicking element it is nonetheless present as though it were in “neat”form for the-purpose of maintaining equilibrium with the vapor phasesuch that the latter is saturated. In accordance with the foregoing,wick 123 is shown in FIG. 2.

The delivery of a precise mass, and thus volume, of air (or other fluid)from the so-called pump module—and in turn the delivery of a like volumeand correlative mass of fluid from the reservoir as aforesaid—can beeffectuated in accordance with the ideal gas law, which is applicable togases under ambient temperatures and pressures. Under the ideal gas lawP*V=n*R*Twherein P=gas pressure, V=gas volume, n=the number of moles of gas,R=the ideal gas constant, and T=absolute temperature. Alternatively, theequation can be rewrittenV/T=n*R/P.It is evident from this relationship that if variables P, n, and R areheld constant, a directly proportional relationship will exist betweenthe temperature of a gas and its volume, with the result that anincrease in temperature will result in a directly proportional increasein volume. Assuming constant values of variables P, n, and R, thisrelationship can be simplified to:V ₁ /T ₁ =V ₂ /T ₂.

For instance, a “pump” cell volume of 1 cc at an ambient temperature of298° K will deliver 0.02 cc of air volume (i.e., ∂V=0.02 cc) if it isheated to a temperature of 304° K (i.e., ∂T=6 degrees). If the headspacevapor concentration is known, then it is possible to calculate the massof vapor delivered to the instrument being calibrated. For example, ifthe headspace vapor concentration is 5000 μg/L and the volume deliveredis 0.00002 L (i.e., 0.02 cc) then the amount of mass delivered is 0.1μg. The amount of vapor mass dispensed by this invention can becalculated using the following expression:m=[(T ₂ −T ₁)/T ₁ ]*V _(pump) *C _(sat)wherein m=the mass of vapor delivered (μg)

T₂=the final temperature of the pump (°K)

T₁=the initial temperature of the pump (°K)

V_(pump)=the volume of the pump (L)

C_(sat.)=the vapor headspace concentration (μg/L)

The absolute accuracy of the mass delivered from vapor reservoir 20 or120 (as the case may be) depends on the absolute temperature andpressure of the vapor reservoir since these parameters determine thesaturated headspace vapor concentration. For the highest accuracy,temperature controller 50 or 150 (again, as the case may be) comprises amicrocomputer with the ability to ascertain the absolute temperature andpressure of the vapor reservoir. Using the temperature and pressureinformation in conjunction with known vapor pressure curves for thereservoir vapor, the microcomputer can calculate the corresponding finaltemperature of the air in the air reservoir 30 or 130 required fordelivery of the precise vapor mass desired. While this extent of controlis not always necessary (for example, where the reservoir temperaturedoes not undergo wide variation or where only semi-quantitative vaporquantities are adequate), it is often advantageous to operate at a highlevel of accuracy.

The invention described herein is susceptible of many modifications andvariations within its scope, and in particular extends to the use of anyone or more of the singular and several features of the foregoingdescription and accompanying drawings and their equivalents.

1. A system for testing the operation of a detection instrument, comprising: a first enclosure having at least two ports and containing fluid comprising a substance detectable in gas form by the instrument, said fluid being present in part as a vapor phase and in part as a liquid phase in equilibrium with one another, said first enclosure being interconnected with the instrument such that the fluid contained in the first enclosure can be dispensed to the instrument via at least one port of said first enclosure; a second enclosure having at least one port and containing either the same or a different fluid in gas form as compared with the first enclosure, said second enclosure being adapted for selective dispensing of a known or ascertainable mass of fluid contained therein via at least one port thereof, and being interconnected with said first enclosure such that said mass can be introduced into the volume within said first enclosure through at least one port thereof, thereby to displace a correlative mass of the vapor phase fluid contained in the first enclosure causing said correlative mass to be dispensed to said instrument; and a valve in communicating relationship with said first enclosure and positioned such that, when the first enclosure is interconnected with said instrument, the valve is interposed between the interconnected first enclosure and instrument, which valve is capable of selectively permitting flow to said instrument of said vapor phase fluid dispensed from the first enclosure upon being displaced by said introduction of fluid from the second enclosure.
 2. The system as defined in claim 1, which further comprises a length of conduit interconnected said second enclosure and said first enclosure, the dimensions and configuration of said length of conduit being such that dead volume and diffusion from or into either of the enclosures is reduced.
 3. The system as defined in claim 1, which further comprises a heating element in thermal contact with the second enclosure such that heat energy from said element is imparted to the contents of said enclosure.
 4. The system as defined in claim 3, which further comprises a processor electrically connected to the heating element, which processor is capable of activating and deactivating the heating element.
 5. The system as defined in claim 4, wherein the processor deactivates the heating element a predetermined time after it activates said element.
 6. The system as defined in claim 4, which further comprises a sensor that is positioned so as to be in contact with the contents of the second enclosure and that is capable of ascertaining the temperature of said contents, said sensor being electrically connected to the processor such that the processor receives signals therefrom permitting the processor to recognize an increase in temperature of said contents and in response to attainment of a predetermined increment of temperature increase deactivates the heating element.
 7. The system as defined in claim 4 wherein the processor is a microcomputer.
 8. The system as defined in claim 1, wherein said valve is a three-way valve having one port communicating with a vent to the ambient atmosphere, one port communicating with the detection instrument, and one port communicating with the interior volume of the first enclosure, said valve being capable of alternating between its normal position in which the port communicating with the detection instrument is closed and another position in which the port communicating with the vent is closed.
 9. The system as defined in claim 8, wherein the valve's movement between its normal position and said other position is electrically actuated.
 10. The system as defined in claim 1, wherein the entire amount of vapor phase fluid dispersed from said first enclosure is analyzed by said instrument and a quantitative measurement thereof is performed.
 11. An apparatus for dispensing a known or ascertainable mass of a fluid in gas form to a detection instrument, comprising: a first enclosure adapted for interconnection with the instrument and capable of containing said fluid when present in part as a vapor phase and in part as a liquid phase in equilibrium with one another; interconnected with the first enclosure, a second enclosure capable of containing either the same or a different fluid in gas form as compared with the first enclosure, said second enclosure being adapted for selective dispensing of a known or ascertainable mass of fluid it is capable of containing for introduction into the volume within said first enclosure thereby to displace a correlative mass of the vapor phase fluid the first enclosure is capable of containing, causing said correlative mass to be dispensed to said instrument; and a valve in communicating relationship with said first enclosure and positioned such that, when the first enclosure is interconnected with said instrument, the valve is interposed between the interconnected first enclosure and instrument, which valve is capable of selectively permitting flow to said instrument of said vapor phase fluid dispensed from the first enclosure upon being displaced by said introduction of fluid from the second enclosure.
 12. The apparatus as defined in claim 11, which further comprises a length of conduit interconnecting said second enclosure and said first enclosure, the dimensions and configuration of said length of conduit being such that dead volume and diffusion from or into either of the enclosures is reduced when the apparatus is connected to the detection instrument and the reservoirs contain said fluid or fluids.
 13. The apparatus as defined in claim 11, which further comprises a heating element in thermal contact with the second enclosure such that heat energy from said element can be imparted to the contents of said enclosure when the apparatus is connected to the detection instrument and the enclosures contain said fluid or fluids.
 14. The apparatus as defined in claim 13, which further comprises a processor electrically connected to the heating element, which processor is capable of activating and deactivating the heating element.
 15. The apparatus as defined in claim 14, wherein the processor deactivates the heating element a predetermined time after it activates said element.
 16. The apparatus as defined in claim 14, which further comprises a sensor that is positioned so as to be in contact with the fluid in the second enclosure and that is capable of ascertaining the temperature of said fluid, said sensor being electrically connected to the processor such that the processor receives signals therefrom permitting the processor to recognize an increase in temperature of said fluid and in response to attainment of a predetermined increment of temperature increase deactivate the heating element.
 17. The apparatus as defined in claim 14, wherein the processor is a microcomputer.
 18. The apparatus as defined in claim 11, wherein said valve is a three-way valve having one port adapted for communicating with a vent to the ambient atmosphere, one port adapted for communicating with the detection instrument, and one port communicating with the first enclosure, said valve being capable of alternating between its normal position in which the port adapted for communicating with the detection instrument is closed and another position in which the port adapted for communicating with the vent is closed.
 19. The apparatus as defined in claim 18, wherein the valve's movement between its normal position and said other position is electrically actuated.
 20. The apparatus as defined in claim 11, wherein the entire amount of vapor phase fluid dispensed from said first enclosure is analyzed by said instrument and a quantitative measurement thereof is performed.
 21. A method of dispensing to a detection instrument a known or ascertainable mass of a fluid in gas form comprising: in a first enclosure interconnected with said instrument and containing said fluid, maintaining conditions such that the fluid is present in part as a vapor phase and in part as a liquid phase in equilibrium with one another; in a second enclosure interconnected with said first enclosure and containing either the same or a different fluid in gas form as compared with the first enclosure, subjecting the fluid in the second enclosure to conditions sufficient to effect an expansion of the fluid in gas form, such that a known or ascertainable mass of said fluid in gas form is dispensed from the second enclosure and introduced into the volume within said first enclosure, thereby to displace a correlative mass of the vapor phase fluid in the first enclosure, causing said correlative mass to be dispensed to the instrument; and selectively permitting said correlative mass to flow through to the instrument.
 22. The method as defined in claim 21, wherein said second enclosure and said first enclosure are interconnected by a length of conduit, the dimensions and configuration of said length of conduit being such that dead volume and diffusion from or into either of the enclosures is reduced.
 23. The method as defined in claim 21, which further comprises imparting heat energy to the fluid in the second enclosure by means of a heating element in thermal contact with the second enclosure.
 24. The method as defined in claim 23, which further comprises activating and deactivating the heating element by means of a processor electrically connected to the heating element.
 25. The method as defined in claim 24, which further comprises deactivating the heating element a predetermined time after activating it.
 26. The method as defined in claim 24, which further comprises ascertaining the temperature of the fluid contained in said second enclosure, by means of a sensor that is positioned so as to be in contact with said fluid, said sensor being electrically connected to the processor such that the processor receives signals therefrom permitting the processor to recognized an increase in temperature of said contents, and deactivating the heating element in response to attainment of a predetermined increment of temperature increase.
 27. The method as defined in claim 24, wherein the processor is a microcomputer.
 28. The method as defined in claim 21, wherein said valve is a three-way valve having one port communicating with a vent to the ambient atmosphere, one port communicating with the measurement instrument, and one port communicating with the interior volume of the first enclosure, said valve alternating between its normal position in which the port communicating with the measurement instrument is closed and another position in which the port communicating with the vent is closed.
 29. The method as defined in claim 28, which further comprises electrically actuating the valve's movement between its normal position and said other position.
 30. The method as defined in claim 21, which further comprises analyzing the entire amount of vapor phase fluid dispersed from said first enclosure in order to perform a quantitative measurement thereof. 